This invention relates to granular or powder detergent compositions, and especially to those compositions intended for use in washing machines having a detergent-dispensing feature.
Granular or powder detergent compositions usually contain, in addition to detergent active materials or surfactants, a detergency builder which functions, among other things, to improve the detergency or cleaning level of the compositions, in comparison to unbuilt compositions. In addition to those materials, conventional additives, such as fabric softeners, whiteners, hydrotropes, bleaching agents, bleach activators, enzymes, soil anti-redeposition agents and the like can also be incorporated into granular detergents.
Recently, there has been a trend within the detergent industry toward powders having higher bulk densities than has been customary in the past, for example, 450 grams per liter and above. This trend is market driven, spurred on by ecological considerations, to produce powdered detergents such that a greater weight of powder can be packed in a given volume of a container or box. However, it has been found that the higher density granules often suffer from poor dispensability in automatic washing machines. In these machines, water enters the dispenser which is charged with the granular detergent and flushes the granules into the wash liquor. If the water does not flush out the entire amount of powder, the powder, when it solidifies, can form relatively large clumps which can eventually block the dispenser and/or the feed pipe from the dispenser to the washing compartment of the machine. This results in a wastage of detergent and a lower level of cleaning, or it requires that the user clean out the dispenser and/or feed line, preferably after each wash cycle. The problem is more prevalent with higher density powders, particularly in non-phosphate, zeolite-containing products, at low wash temperatures, including cold-water washes, and at low water pressure and/or water flow rates; and is most extreme in formulas with a high ratio of nonionic, e.g., more than 90% nonionic with respect to ionic surfactant. While the phenomenon is not fully understood, solubilization of at least a portion of the granular detergent to form a pasty-or syrupy-consistency slurry before the granules have been washed out of the dispenser into the wash liquor appears to be a contributing factor.
Several proposals have been offered for improving the dispensability of granular detergent compositions. European Patent Application 360,330 (Unilever PLC) discloses a process for the preparation of a detergent powder, which includes the steps of preparing an intermediate powder, and spraying onto the intermediate powder an intimate mixture of a C.sub.8-22 fatty acid and a liquid or liquifiable nonionic surfactant. The final detergent powder is said to have a dynamic flow rate of at least 90 ml/s. Garner-Gray et al., U.S. Pat. No. 4,966,606, propose a method for improving dispensability of granular detergent compositions containing sodium carbonate and finely-divided calcite by providing detergent granules or particles which have a mean size of at least 500 microns, with less than two percent by weight of the particles having a size of less than 50 microns. The '606 patent also references other proposals, including those of British Patent Specification No. GB 212093-A (addition of a siliconate to bentonite-containing powders) and European Patent Specification No. EP 49920 (addition of hydrophobic material such as calcium stearate to phosphate/silicate granular dishwashing compositions). Seiter et al., U.S. Pat. No. 4,849,125, propose to employ a powder component which has a certain grain specification and certain additives and quantitative ratios in order to avoid subsequent separation of the granulate and optimize detergent properties. The powders are subsequently impregnated with nonionic surfactant.